Niamh/Neve: depending on where you live, Niamh would have a heck of a time getting people to spell and pronounce her name right; Neve, though, is beautiful and exotic, while being easily spelled and pronounced.

Pearl: I would LOVE to see this on a child! It's familiar and recognizable, but is WAY underused. I've never met a Pearl of any age.

Ada: too close to the trendy Ava and Addison for my liking, and I think it wouldn't catch people's attention.

Keira: This has a much different feel than the vintage Pearl and Ada. Very contemporary-sounding and ALMOST a touch exotic. I do like it a lot.

Wren: this one just feels incomplete to me. It's a pretty word to see written out, but the sound lacks substance.

Margot: I don't like that this looks like "maggot" written out, and the sound has always struck me as odd and unappealing.

From your list I like Niamh and Keira. My cousin is Niamh, and yes she gets spelling issues a LOT, but she loves her name anyway. Pronunciation is only an issue when someone reads her name first, which honestly doesn't happen much- doctor appointments and first day of school really. Also we live in a part of the US where the majority of people are of Irish decent, so a lot of people are familiar with the name to begin with. Keira is much more mainstream, but still a little unexpected which I think is nice.